Monday, July 28, 2014

From bone to zone: Focus on navicular-type lameness has evolved from concentrating on identifying bone defects visible in radiography to a more dynamic approach to also detect possible soft tissue injury, deteriorating hoof condition and age- or sport-related stress factors. The navicular bone is circled in this distal limb bone model at the University of Nottingham Vet School.

The landscape of treatment options for equine navicular syndrome is set to change this year, as the U.S. Food and Drug Agency (FDA) recently approved two drugs for use in the treatment of this complex lameness problem in the horse's foot. "Tildren" and "Osphos" are two specific medications that cleared the difficult hurdles of the FDA approval process in May 2014.

Each of these drugs has a different active ingredient, but both belong to a class of drugs known as bisphosphonates. These drugs are also used in human medicine and are commonly prescribed for treatment of osteoporosis.

In this age of "evidence-based medicine", it should be noted that one of the first things that the FDA notes in its documentation is that the mechanism of bisphosphonates in navicular syndrome is not known.

The FDA describes the role of the drugs as being to "control the clinical signs" of navicular syndrome.

Bisphosphonates have been available to US veterinarians for treating navicular syndrome on a limited basis during the FDA approval process, so it is very possible that Hoofcare and Lameness readers are already familiar with the medications and their use, and the types of questions that horse owners are likely to have about the medications.

While virtually all aspects of what causes and constitutes what many still call "navicular disease" remain open to great (and lively) debate among veterinarians and farriers, advances in imaging, medication and hoofcare are assisting in providing at least cautiously optimistic management of many cases.

The navicular bone is a key part of the coffin joint in the foot, and is surrounded by multiple structures that can facilitate or impede its smooth function, as may damage to the bone itself. When pain is localized to the navicular "zone", a diagnosis of navicular syndrome is always a possibility. This image is a plastinated hoof tissue specimen created by anatomist Christoph von Horst, DVM, PhD of HC Biovision in Germany.

"From bone to zone" describes the change in focus for navicular-type pain over the past 30 years, when radiographic evidence was usually the first and only proof that a horse had a bone disease. But even then, damage to the navicular bone was often visible in screening images of sound horses, while lame horses might have flawless views. MRI was the imaging technique that came along at the right time to serve a population of horses plagued with caudal foot pain.

The way that certain horses respond positively to a specific type of therapeutic shoeing while others do not is still part of the enigma of this type of lameness.

Many lameness cases that would have received the dreaded diagnosis of navicular "disease" years ago are now described with varying types of chronic caudal foot pain, or can be identified with very specific lesions of the deep digital flexor tendon or injuries to the navicular bursa or strain in specific ligaments. Classic navicular bone lesions and disease conditions of the bone do still exist and some cases even have been shown to have multiple sources of injury or types of damage.

Tildren and Osphos are likely to remain very expensive treatments that will be options only for those horse owners able to afford them. The challenge to veterinarians will be in obtaining an accurate diagnosis of the horse's problem and determining whether or not these medications are appropriate for the case, since horse owners are likely to be curious about them. In other cases, the challenge will be in explaining that the medication might be appropriate for the case, but not affordable for the owner.

Just as with joint injection, PRP, and other treatments, proceeding on a path with bisphosphonates without recognizing and addressing any sub-optimal hoof issues and mapping out a plan for the recovery of the foot itself will lead to eventual disappointment. All too often, the basic needs of the hoof itself are addressed only as a last resort, after all the expensive options have been tried.

Navicular syndrome will never likely be a simple lameness condition for anyone involved in diagnosing, treating or managing it, and least of all for the horse affected by it. Horse owners must not give in to wishful thinking that these (or any) medications can cure a horse's lameness issues without a full treatment program that includes evaluating the horse's conformation, work load, choice of sport, stabling routine or hygiene, training surface, and diligence or appropriateness of hoofcare to determine how some of these factors may have been involved in the development of lameness or deterioration of foot condition.

Tildren has also been tested in Europe for use in other equine lameness problems, such as hock spavin or back pain, but its use in the United States has only been approved for navicular syndrome. The drug has a very specific application protocol that veterinarians follow.

Under the Freedom of Information Act, summaries of the application and approval documents for the medications are posted for public viewing on the FDA website.

Disclosure of Material Connection: The Hoof Blog (Hoofcare Publishing) has not received any direct compensation for writing this post. Hoofcare Publishing has no material connection to the brands, products, or services mentioned, other than products and services of Hoofcare Publishing. I am disclosing this in accordance with the Federal Trade Commission’s 16 CFR, Part 255: Guides Concerning the Use of Endorsements and Testimonials in Advertising.

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